The use of electro-luminescent (EL) panels, particularly in portable electronic derives such as keyboards of laptop and desktop computers, requires meeting various standard safety tests. In order to produce a high level of backlighting, a high peak to peak voltage is necessary. To avoid electrical shock, organizations like UL (Underwriters Laboratories), require that the inverter, used to power the EL panel(s), provides the power necessary such that the clearance and creepage distance between the high voltage output of the EL panel and its surroundings (enclosure, printed circuit board and connector) do not create a hazardous condition (UL 60950). The requirement of a safety space usually needs 4-8 mm. For portable and lightweight devices where space is at a premium, it is difficult to meet such standards. The alternative method to meet such standard is to provide limited current circuit (LCC) in the inverter. The equivalent impendence of a human body is about 2000 ohms. For a 2000 ohm load between outputs or output to ground, a maximum peak current flow should not exceed 0.7 mA.
Conventional single ended autotransformer type inverters inhibit the oscillation as the output load is shorted, but do not take a 2000 ohm load into account. Such an inverter would protect itself from an output short circuit, but would not prevent an electrical shock to the human body upon contact with the output of the inverter under normal conditions.
Thus, there is a need to provide an inverter circuit with capability to limit current such that a maximum peak current flow to ground does not exceed 0.7 mA.